1. Field of the Invention
The present invention relates to a recording apparatus that records by use of a recording head on a recording medium.
2. Related Background Art
FIG. 6 is a perspective view that shows the outer appearance of an ink jet recording apparatus in general.
In FIG. 6, a reference numeral 101 designates the chassis, which is formed by sheet metal work. The chassis 101 is provided with various parts to structure the recording apparatus. A reference numeral 102 designates a sheet-feeding device to stack recording sheets thereon, and feeds each of them to the recording portion after separating them one by one at the time of recording; 103, a carriage that mounts both an ink tank and a recording head (neither shown) and performs recording by discharging ink from the recording head to the recording sheet while scanning in the direction B along the metallic carriage shaft 104; and 107, a pinch roller holder attached to the chassis 101, which is provided with plural pinch rollers 108 rotational in the sheet conveying direction, and which presses the pinch rollers 108 against a sheet conveying roller 105 by use of pinch roller springs 120. The pinch rollers 108 and the sheet conveying roller 105 pinch the recording sheet to convey it as the sheet conveying roller 105 rotates. A reference numeral 106 designates a platen having ribs 106a, and the recording sheet is conveyed on the ribs 106a. 
Since the recording sheet is not rigid, it is not necessarily practicable to convey the sheet with the degree of parallelism being kept exactly during the conveyance thereof. Particularly, in the case of the recording apparatus of ink jet type that records by discharging ink to a recording sheet, the moisture contained in ink results in the expansion of the recording sheet to make it wavy sometimes. The edges of the recoding sheet, in particular, tend to float, and in the worst case, rubbing takes place between the recording head and the sheet to disturb recording eventually.
FIG. 7 and FIG. 8 are perspective views that illustrate the principle part of the conventional structure that provides the prevention of rubbing between a recording sheet and a recording head. FIG. 7 shows the right edge side of the recording sheet, and FIG. 8 shows the left edge side thereof.
In FIG. 7, a reference numeral 109 designates a recording sheet, and 110, a right-side sheet pressure plate that engages with the platen 106 by use of a nail. The right edge 109a of the recording sheet 109 passes under the right-side sheet pressure plate 110 when the recording sheet is conveyed, thus preventing the right edge 109a of the recording sheet from floating and rubbing against the recording head.
For many recording apparatuses, the position of a recording sheet is determined with the right edge of the recording sheet as a reference. In this case, the widthwise differences of recording sheets present the positional differences at the right edge thereof. For example, an A-4 size and a LTR size (LETTER size) present a difference of approximately 6 mm in positions at the left edges of the recording sheets. Therefore, a left-side sheet pressure plate 111 has an extended left-edge pressure portion 111a for use with A-4 size media and a left-edge pressure portion 111b for use with LTR size media.
If a left-side sheet pressure plate for use with an A-5 or narrower sized recording sheet is arranged at a position corresponding to the left edge thereof, the A-4 size and other wider recording sheets abut against such left-side sheet pressure plate eventually. In this case, therefore, a sheet-pressure formation 107a, which is configured integrally with the pinch roller holder, 107 (the same in the case of mylar sheet and others), is arranged at the left edge of each size of the narrower recording sheets. Then, it is arranged to press the left edge of the corresponding recording sheet with the resiliency of such sheet-pressure formation.
As described above, however, if it is intended to press the left edge of each recording sheet having different width by use of one member, such as the left-side sheet pressure plate 111, the configuration thereof becomes complicated. Also, the sheet pressure plate is positioned between the recording sheet and the recording head. As a result, the plate thickness should be as thin as 0.2 mm to 0.3 mm approximately, and there is a possibility that deformation takes place in the A-4 size pressure portion 111a. 
Also, the sheet pressure formation 107a that presses the left edge of recording sheets each having various widths is arranged to press the recording sheet with the resilient force to be generated by the deformation thereof. Therefore, this becomes resistance to the conveyance of the recording sheet to result in the possibility that the conveyance precision is degraded. If the number of the sheet pressure formations 107a increases, the potential of such degradation should become more inevitable.